First Report of Treatment-Emergent Resistance to Cefepime-Zidebactam in Pseudomonas aeruginosa

We describe the first case of cefepime-zidebactam treatment-emergent resistance associated with clinical failure in a patient with Pseudomonas aeruginosa pneumonia. During treatment, cefepime-zidebactam minimum inhibitory concentrations increased from 8/8 to 32/32 mg/L. Whole-genome sequence analysis showed new mutations in the MexAB-OprM efflux operon that were associated with cross-resistance to ceftazidime-avibactam and imipenem-relebactam.